Styrofoam effects on ammo?


I recently bought a box of Thompson Contender 44 Mag shotshells that were in a styrofoam tray. The blue plastic shot capsule has a spotty, white substance on them that can be scratched off with the fingernail and does not seem to be eating into the plastic. Furthermore, there is a small ammount of gray/white dust in each pocket of the styrofoam tray.
Any ideas what this is and if it will hurt the cartridge?
Suggestions for cleaning it off the plastic without hurting it? Tried vinager and rubbing with cloth but not very effective.

The cartridge on the left is a .357 Contender round that came from a paper tray and shows no sign of this effect. The .44s fit very tightly in these pockets.

This is the dust from 2 pockets. Its obviously grayer in color than styrofoam so I wonder if its oxide from the lead pellets and unrelated to the stuff on the outside?


Powder maybe contains buffer material from inside the shell capsule? Haven’t shot one of those in years (missing my Contender today!).


I don’t see any sign of filler/buffer material in these. After more study and thought, think its oxidation of the lead. The top of the capsules have open slots where atmosphere can get in, dust can get out.

Surely someone has an opinion on the white stuff on the outside of the shot capsules?


Sounds like the dust from the lead oxidation. I don’t believe that these capsules are supposed to have any openings on the top.



A couple other guesses (perhaps WAGs!):

It looks like the lead pellets are protruding through the wall of the capsule as they expand while growing the white stuff (oxide and carbonate of lead). This could cause the blue plastic to become opaque white as it stretches at those points. Another possibility is there is some reaction going on where the blue plastic pushed against the polystyrene foam container is being attacked by residule components of the foam’s manufacture. Solvents like methylene chloride are used to make the foam and I think that is like airplane glue on plastic. Might be enough left in the foam to work on the capsules over time.

Sucks that that’s hapening in the original packaging…



Guy, its quite possible that these are splits in the top but I’m not certain that they are, they look like they belong.

The white substance on the outside is not effecting the plastic… yet… so think I’ll try to clean them with a damp, soapy cloth and after they are dry, I’ll store them outside that styrofoam.


The splits in the nose were there when they were made. They are normal, especially on the .44 Mags.